According to some estimates, oil sands, also known as tar sands or bituminous sands, may represent up to two-thirds of the world's petroleum. Oil sands resources are relatively untapped. Perhaps the largest reason for this is the difficulty of extracting bitumen from the sands. Mineable oil sand is found as an ore in the Fort McMurray region of Alberta, Canada, and elsewhere. This oil sand includes sand grains having viscous bitumen trapped between the grains. The bitumen can be liberated from the sand grains by slurrying the as-mined oil sand in water so that the bitumen flecks move into the aqueous phase for separation. For the past 40 years, bitumen in McMurray oil sand has been commercially recovered using the original Clark Hot Water Extraction process, along with a number of improvements. Karl Clark invented the original process at the University of Alberta and at the Alberta Research Council around 1930 and improved it for over 30 years before it was commercialized.
In general terms, the conventional hot water process involves mining oil sands by bucket wheel excavators or by draglines at a remote mine site. The mined oil sands are then conveyed, via conveyor belts, to a centrally located bitumen extraction plant. In some cases, the conveyance can be as long as several kilometers. Once at the bitumen extraction plant, the conveyed oil sands are conditioned. The conditioning process includes placing the oil sands in a conditioning tumbler along with steam, water, and caustic soda in an effort to disengage bitumen from the sand grains of the mined oil sands. Further, conditioning is intended to remove oversize material for later disposal. Conditioning forms a hot, aerated slurry for subsequent separation. The slurry can be diluted for additional processing, using hot water. The diluted slurry is then pumped into a primary separation vessel (PSV). The diluted hot slurry is then separated by flotation in the PSV. Separation produces three components: an aerated bitumen froth which rises to the top of the PSV; primary tailings, including water, sand, silt, and some residual bitumen, which settles to the bottom of the PSV; and a middlings stream of water, suspended clay, and suspended bitumen. The bitumen froth can be skimmed off as the primary bitumen product. The middlings stream can be pumped from the middle of the PSV to sub-aeration flotation cells to recover additional aerated bitumen froth, known as a secondary bitumen product. The primary tailings from the PSV, along with secondary tailings product from flotation cells are pumped to a tailings pond, usually adjacent to the extraction plant, for impounding. The tailings sand can be used to build dykes around the pond and to allow silt, clay, and residual bitumen to settle for a decade or more, thus forming non-compacting sludge layers at the bottom of the pond. Clarified water eventually rises to the top for reuse in the process.
The bitumen froth is treated to remove air. The deaerated bitumen froth is then diluted with naptha and centrifuged to produce a bitumen product suitable for upgrading. Centrifuging also creates centrifugal tailings that contain solids, water, residual bitumen, and naptha, which can be disposed of in the tailings ponds.
More than 40 years of research and many millions of dollars have been devoted to developing and improving the Clark process by several commercial oil sands operators, and by the Alberta government. Research has largely been focused on improving the process and overcoming some of the major pitfalls associated with the Clark process. Some of the major pitfalls are:                1. Major bitumen losses from the conditioning tumbler, from the PSV and from the subaeration cells.        2. Reaction of hot caustic soda with mined oil sands result in the formation of naphthenic acid detergents, which are extremely toxic to marine and animal life, and require strict and costly isolation of the tailings ponds from the environment for at least many decades.        3. Huge energy losses due to the need to heat massive amounts of mined oil sands and massive amounts of water to achieve the required separation, which energy is then discarded to the ponds.        4. Loss of massive amounts of water taken from water sources, such as the Athabasca river, for the extraction process and permanently impounded into the tailings ponds that can not be returned to the water sources on account of its toxicity. For example, to produce one barrel of oil requires over 2 barrels of water from the Athabasca River.        5. The cost of constructing and maintaining a large separation plant.        6. The cost of transporting mined oil sands from a remote mining location to a large central extraction plant by means of conveyors. Additionally, the conveyors can be problematic.        7. The cost of dilution centrifuging.        8. The cost of naphtha recovery.        9. The cost of maintaining and isolating huge tailings ponds.        10. The cost of preventing leakage of toxic liquids from the tailings ponds.        11. The cost of government fines when environmental laws are breached.        12. The eventual cost of remediation of mined out oil sands leases and returning these to the environment in a manner acceptable to both the Alberta and the Canadian government.        13. The environmental impact of the tailings ponds.        
Some major improvements have been made that included lowering the separation temperature in the tumbler, the PSV, and the flotation cells. This reduced the energy costs to a degree but also required the use of larger tumblers and the addition of more air to enhance bitumen flotation. Another improvement eliminated the use of bucket wheel excavators, draglines and conveyor belts to replace these with large shovels and huge earth moving trucks, and then later to replace some of these trucks with a slurry pipeline to reduce the cost of transporting the ore from the mine site to the separation plant. Slurry pipelines eliminate the need for conditioning tumblers but require the use of oil sand crushers to prevent pipe blockage and require cyclo-feeders to aerate the oil sand slurry as it enters the slurry pipeline, and may also require costly compressed air injection into the pipeline. Other improvements included tailings oil recovery units to scavenge additional bitumen from the tailings, and naptha recovery units for processing the centrifugal tailings before these enter the tailings ponds.
More recent research is concentrating on reducing the separation temperature of the Clark process even further and on adding gypsum or flocculants to the sludge of the tailings ponds to compact the fines and release additional water. However, adding gypsum hardens the water and this can require softening of the water before it can be recycled to the extraction plant. Most of these improvements have served to increase the amount of bitumen recovered and reduce the amount of energy required, but have increased the complexity and size of the commercial oil sands plants.
One particular problem that has vexed commercial mined oil sands plants is the problem of fine tailings disposal. In the current commercial process, mined oil sands are mixed and stirred with hot water, air, and caustic soda to form a slurry that is subsequently diluted with cooler water and separated in large separation vessels. In these vessels, air bubbles attach to bitumen droplets of the diluted slurry and cause bitumen product to float to the top for removal as froth. Caustic soda serves to disperse the fines to reduce the viscosity of the diluted slurry and allows the aerated bitumen droplets to travel to the top of the separation vessels fast enough to achieve satisfactory bitumen recovery in a reasonable amount of time. Caustic soda serves to increase the pH of the slurry and thereby imparts electric charges to the fines, especially to the clay particles, to repel and disperse these particles and thereby reduce the viscosity of the diluted slurry. For most oil sands without caustic soda, the diluted slurry would be too viscous for effective bitumen recovery. It can be shown from theory or in the laboratory that for an average oil sand, it takes five to ten times as long to recover the same amount of bitumen if no caustic soda is added to the slurry. Such a long residence time would make commercial oil sands extraction much more expensive and impractical.
While caustic soda is beneficial as a viscosity breaker in the separation vessels for floating off bitumen, it is environmentally very detrimental. At the high water temperatures used during slurry production it reacts with naphthenic acids in the oil sands to produce detergents that are highly toxic. Not only are the tailings toxic, but also the tailings fines will not generally settle. Tailings ponds with a circumference as large as 20 kilometers are required at each large mined oil sands plant to contain the fine tailings. Coarse sand tailings are used to build huge and complex dyke structures around these ponds.
Due to the prior addition of caustic soda, the surfaces of the fine tailings particles are electrically charged, which in the ponds, causes the formation of very thick layers of microscopic card house structures that compact extremely slowly and take decades or centuries to dewater. Many millions of dollars per year have been and are being spent in an effort to maintain the tailings ponds and to find effective ways to dewater these tailings. Improved mined oil sands processes must be commercialized to overcome the environmental problems of the current plants. One such alternate method of oil sands extraction is the Kruyer Oleophilic Sieve process invented in 1975.
Like the Clark Hot Water process, the Kruyer Oleophilic Sieve process originated at the Alberta Research Council and a number of Canadian and U.S. patents were granted to Kruyer as he privately developed the process for over 30 years. The first Canadian patent of the Kruyer process was assigned to the Alberta Research Council and, and all subsequent patents remain the property of Kruyer. Unlike the Clark process, which relies on flotation of bitumen froth, the Kruyer process uses a revolving apertured oleophilic wall (trade marked as the Oleophilic Sieve) and passes the oil sand slurry to the wall to allow hydrophilic solids and water to pass through the wall apertures whilst capturing bitumen and associated oleophilic solids by adherence to the surfaces of the revolving oleophilic wall.
Along the revolving apertured oleophilic wall, there are one or more separation zones to remove hydrophilic solids and water and one or more recovery zones where the recovered bitumen and oleophilic solids are removed from the wall. This product is not an aerated froth but a viscous liquid bitumen.
A bitumen-agglomerating step normally is required to increase the bitumen particle size before the slurry passes to the apertured oleophilic wall for separation. Attention is drawn to the fact that in the Hot Water Extraction process the term “conditioning” is used to describe a process wherein oil sands are gently mixed with controlled amounts water in such a manner as to entrain air in the slurry to eventually create a bitumen froth product from the separation. The Oleophilic Sieve process also produces a slurry when processing mined oil sands but does not “condition” it. Air is not required, nor desired, in the Oleophilic Sieve process. As a result, the slurry produced for the Oleophilic Sieve, as well as the separation products, are different from those associated with the conventional Hot Water Extraction process. The Kruyer process was tested extensively and successfully implemented in a pilot plant with high grade mined oil sands (12 wt % bitumen), medium grade mined oil sands (10 wt % bitumen), low grade oil sands (6 wt % bitumen) and with sludge from commercial oil sands tailings ponds (down to 2% wt % bitumen), the latter at separation temperatures as low as 5° C. A large number of patents are on file for the Kruyer process in the Canadian and U.S. Patent Offices. These patents include: CA 2,033,742; CA 2,033,217; CA 1,334,584; CA 1,331,359; CA 1,144,498 and related U.S. Pat. No. 4,405,446; CA 1,141,319; CA 1,141,318; CA 1,132,473 and related U.S. Pat. No. 4,224,138; CA 1,288,058; CA 1,280,075; CA 1,269,064; CA 1,243,984 and related U.S. Pat. No. 4,511,461; CA 1,241,297; CA 1,167,792 and related U.S. Pat. No. 4,406,793; CA 1,162,899; CA 1,129,363 and related U.S. Pat. No. 4,236,995; and CA 1,085,760.
While in a pilot plant, the Kruyer process has yielded higher bitumen recoveries, used lower separation temperatures, was more energy efficient, required less water, did not produce toxic tailings, used smaller equipment, and was more movable than the Clark process. There were a number of drawbacks, though, to the Kruyer process.
One drawback to the Kruyer process is related to the art of scaling up. Scaling up a process from the pilot plant stage to a full size commercial plant normally uncovers certain engineering deficiencies of scale such as those identified below.
Commercial size apertured drums that may be used as revolving apertured oleophilic walls require very thick perforated steel walls to maintain structural integrity. Such thick walls increase retention of solids by the bitumen and may degrade the resulting bitumen product. Alternately, apertured mesh belts may be used as revolving apertured oleophilic walls. These have worked well in the pilot plant but after much use, have tended to unravel and fall apart. This problem will likely be exacerbated in a commercial plant running day and night. Rugged industrial conveyor belts are available. These are made from pre-punched serpentine strips of flat metal and then joined into a multitude of hinges by cross rods to form a rugged industrial conveyor belt. Other industrial metal conveyor belts are made from flattened coils of wire and then joined into a multitude of hinges by cross rods to form the belts. Both types of metal belts were tested and have stood up well in a pilot plant. However, it was difficult and energy intensive to remove most of the bitumen product in the recovery zone from the surfaces of the belts before these revolved back to the separation zone.
Bitumen agglomerating drums using oleophilic free bodies, in the form of heavy oleophilic balls that tumbled inside these drums worked very well in the pilot plant. However commercial size agglomerators using tumbling free bodies may require much energy and massive drum structures to contain a revolving bed of freely moving heavy oleophilic balls with adhering viscous cold bitumen to achieve the desired agglomeration of dispersed bitumen particles.
As such, improvements to methods and related equipment for recovery of bitumen from oil sands continue to be sought through ongoing research and development efforts.